The present invention relates to drill pipe and more particularly to multiple wall drill pipe having means for releasably connecting an inner pipe member to an outer pipe member of the multiple wall drill pipe.
Multiple wall drill pipe, e.g., such as that shown in U.S. Pat. Nos. 1,547,461; 1,909,075; 2,850,264; 3,208,539; and 3,664,441, has been used for many years in both conventional and reverse circulation drilling operations. Such multiple wall pipe is conventionally made of an outer pipe member and an inner pipe member disposed concentrically within the outer pipe member and longitudinally fixed thereto such as by straps welded to the inner wall of the outer pipe member and the outer wall of the inner pipe member at one or more locations along the length of the multiple wall pipe. Sections of the multiple wall pipe are adapted to be joined in longitudinal alignment to form a drill pipe string extending from a cutting bit to the surface of the ground where the drilling operation is being conducted. Two continuous flow passages are formed in the multiple wall pipe, a central passage defined by the inner surface of the inner pipe members and an annular passage formed between the outer surfaces of the inner pipe members and the inner surfaces of the outer pipe members. These passages are used to transport a drilling fluid from the ground surface to the drill bit and then back to the surface. For example, in a reverse circulation drilling operation, drilling fluid in injected into the upper end of the annular passage under pressure, is forced downwardly therethrough to the drill bit and then returns to the surface through the central passage along with fragments generated by the drilling operation.
In rotary drilling operations using multiple wall drill pipe, torque is transmitted to the drill bit through the outer pipe members. It has been determined that if the inner pipe members are fixedly non-rotatably rigidly connected by welds to the outer pipe members, relatively high torsional stresses may be transmitted from the outer pipe member to the inner pipe member through the fixed non-rotatable rigid connections during rotary drilling operations with resulting pipe failures caused by torsional stress and metal fatigue. Such failures usually occur in an area at or adjacent the fixed welded connection between the inner and outer pipe members. In some situations, such failures may be repaired by replacement of the inner pipe member and rewelding of the fixed connections. However, to the extent that repair of damaged sections of conventional multiple wall pipe has been possible at all, such repair has been extremely difficult and costly. Typical procedures for repair of broken or damaged connections between the inner and outer pipe have involved wall cutting operations such as with a torch, to effect necessary repair or replacement of component parts. This procedure is frequently found to be either mechanically or economically prohibitive, resulting in complete replacement of the damaged section with a new section of multiple wall pipe without salvage of either the inner or outer pipe member.
The present invention involves new and improved connecting means for releasably and rotatably connecting the inner pipe member to the outer pipe member to enable repair and/or replacement while holding the inner pipe member in fixed axial relationship under force loads applied in use during a drilling operation and while enabling relative rotary movement between the inner pipe member and the outer pipe member to relieve torsional stresses encountered during use, the releasable connecting means permitting the removal of the inner pipe member from the outer pipe member by relative axial displacement therebetween caused by application of only an axially directed force load in excess of the axially directed force loads applied to the pipe during use in a drilling operation. In general, the connecting means comprises a plurality of axially spaced sets of resilient compressible axially spaced connecting members mounted in corresponding axially spaced sets of axially spaced inner and outer groove means providing a plurality of axially interengaged stop surfaces which prevent relative axial movement between the inner pipe and the outer pipe in either direction occasioned by any axial forces applied thereto in use during a drilling operation whereby the inner pipe is located in fixed axial position relative to the outer pipe at more than one location along the length of the pipes.
In the illustrative and presently preferred embodiment of the invention there are at least two sets of connecting members and associated grooves with one set located adjacent one end of the pipe section and the other set located adjacent the other end of the pipe section to axially fix each end portion of the inner pipe member relative to each end portion of the outer pipe member. Each set of connecting members and associated grooves comprise three equally axially spaced inner groove means formed in the outer periphery of the inner pipe and three similarly equally axially spaced outer groove means formed in the inner periphery of a connecting sleeve means fixedly attached to the outer pipe member. The connecting members, which are resilient compressible O-ring members, are mounted in corresponding axially aligned ones of the inner and outer connecting groove means during assembly so as to connect and support the inner pipe member relative to the outer pipe member after assembly and during use in a manner preventing relative axial displacement while permitting relative rotational displacement during use and while enabling disassembly of the inner and outer pipe for repairs or the like upon application of axially directed forces in excess of any axially directed forces normally encountered during usage.